Abstract
Clean surfaces produced by cleavage or ion bombardment and annealing mostly show atomic steps. With a new derivation of the LEED pattern of a stepped surface it is now possible to predict and evaluate also the pattern of a surface on a non-primitive lattice. With the use of high precision LEED data depression of the edge atoms of about 0.25 Å is supported by several independent observations. On cleaved silicon and germanium surfaces the step density is determined for each spot of the surface. At clean cleaved silicon surfaces the photo surface voltage has been measured by scanning the surfaces with an electron beam. A correlation between the photo surface voltage and the angle of inclination of the respective spot of the surface towards the (111) face reveals the existence of one-dimensional surface states ("edge states"). It is therefore important to know the existence and properties of atomic steps on clean surfaces in both structural and electronic respects.